1. Field of the Invention
This invention relates to an image holding member for holding electrostatic images or toner images.
2. Description of the Prior Art
Electrostatic images or toner images can be formed by various processes. As image holding member on which electrostatic images or toner images are formed, there may be mentioned an image holding member called "electrophotographic photosensitive member" having a photoconductive layer and an image holding member having no photoconductive layer.
An image holding member is usually composed of a support and an image holding layer overlying the support.
An electrophotographic photosensitive member may be in various forms depending upon the desired characteristics and the kind of electrophotographic process to be applied. Representative electrophotographic photosensitive members are a photosensitive member composed of a support and a photoconductive layer is an image holding layer and a photosensitive member composed of a photoconductive layer as an image holding layer and an insulating layer thereon. These electrophotographic photosensitive members are widely used.
A photosensitive member composed of a support and a photoconductive layer may be used for forming images by a most popular electrophotographic process, i.e., charging, imagewise exposure and developing, if desired, transferring the images.
The insulating layer of a photosensitive layer having an insulating layer serves to protect the photoconductive layer, improve mechanical strength of the photoconductive layer and dark decay characteristics, or fits the photosensitive member to a particular photographic process. Representative photosensitive members having such insulating layer and electrophotographic processes using such photosensitive members are disclosed in Japanese Patent Publication No. 16429/1966 and U.S. Pat. Nos. 2,860,048, 3,146,145, 3,607,258, 3,666,363, 3,734,609, 3,457,070 and 3,124,456.
An electrophotographic process is applied to the electrophotographic photosensitive member to produce electrostatic images and the electrostatic images are visualized by development.
Representative image holding members having no photoconductive layer are those having an insulating layer as an image holding layer. Representative usages of such image holding member are as shown below.
(1) For example, Japanese Patent Publication Nos. 7115/1957, 8204/1957 and 1559/1968 disclose an electrophotographic process comprising transferring electrostatic images formed on an electrophotographic photosensitive member, developing the electrostatic images and then transferring the toner images thus developed to a recording member for the purpose of improving repeatability of using the electrophotographic photosensitive member. An image holding member used for this process is an example of the image holding member having no photoconductive layer.
(2) For example, U.S. Pat. Nos. 3,680,954 and 3,645,614 and U.S. Ser. No. 771,309 filed on Feb. 23, 1977 disclose another electrophotographic process comprising forming electrostatic images on an image holding member having no photoconductive layer corresponding to electrostatic images formed on an electrophotographic photosensitive member. To an electrophotographic photosensitive member in a form of a screen having many fine openings is applied a particular electrophotographic process to produce electrostatic images, and a corona charging treatment is applied to the image holding member having no photoconductive layer by means of the electrostatic images, and the ion stream of corona is modulated to produce electrostatic images on the image holding member having no photoconductive layer followed by developing with toner, and then the images thus developed are transferred to a recording member to produce final images. The image holding member used in this electrophotogrphic process is another example of the image holding member having no photoconductive layer.
(3) Further, according to the other electrophotographic process, toner images formed on an electrophotograhic photosensitive member or an image holding member having no photoconductive layer are not directly transferred to a recording member, but to the other image holding member having no photoconductive layers, and then the toner images thus transferred are transferred to a recording member and fixed. The image holding member used in the above mentioned electrophotographic process is also an example of the image holding member having no photoconductive layer.
This electrophotographic process is particularly suitable for producing color images or high speed copying. Recording members are usually composed of a highly flexible material of less dimensional stability such as paper, film and the like. Therefore, a process comprising transferring each of three colors to a recording member subsequently by registering cannot produce exactly registered three color images. It is preferable to transfer the three colors to an image holding member composed of a material which is substantially free from deformation and then transferring the resulting three-colored images at once to a recording member. This process can produce more exactly registered color images.
Further, it is effective for high speed copying to transfer toner images to a recording member by means of an image holding member.
(4) A still further process comprises applying an electric signal to a multiple stylus electrode to produce electrostatic images on the surface of an image holding member having no photoconductive layer in accordance with the electric signals and developing the electrostatic images. The image holding member used in this process is also an example of the image holding member having no photoconductive layer.
Image holding members used for electrophotography are subjected to various electrical and mechanical forces such as corona charging treatment, cleaning, developing and the like so that they are often damaged. And once image holding members are damaged, image quality formed is remarkably lowered. Therefore, an image holding member is strongly demanded which has excellent electric impact resistance and mechanical impact resistance and further excellent electric charge retentivity. However, such excellent image holding members have not been produced.